This invention relates to measurement systems of the type in which a sensor, the electrical resistance of which varies as a function of the parameter being measured, is electrically connected in one arm of a bridge circuit, often through a transmission line sufficiently long to require consideration of its electrical impedance in the bridge design. The invention is particularly applicable to oceanography systems in which thermisters are used to measure water temperature, and is an improvement upon what is disclosed in U.S. Pat. Nos. 3,221,556; 3,339,407; and Re 27,103. Many systems to which the invention is applicable include a second long transmission wire connected in a second arm of the bridge, the two transmission wires having equal resistances R.sub.c and being arranged so that any resistance-changing conditions affect both wires equally during operation of the system. Third and fourth arms are respectively connected to the first and second arms at first and second control nodes. A reference voltage is introduced into the bridge, and active control circuitry is provided to balance the bridge by controlling the currents in the bridge arms. The bridge current is then measured to provide a readout indicative of the value of the parameter being measured.